1. Field of the Invention
The present invention is in the field of machine tools for cutting, and more particularly relates to a router bit that is adjstable and that remains substantially counterbalanced for all conditions of adjustment. A router bit is normally held in a chuck for rotation about an axis as a work piece is fed into the path of the cutting edge of the router bit in a direction perpendicular to the axis, for the purpose of cutting a groove, called a dado, across the face of the work piece.
2. The Prior Art
The present invention falls into the class of machine tools in which an arbor is adjustably positioned and then fixed in a bore whose axis is parallel to but displaced from the axis of rotation of the tool. A cutting blade affixed to the arbor extends in a direction perpendicular to the axis of the bore. The diameter of the cut is adjusted prior to use by rotating the cutting edge about the axis of the bore.
This type of cutting tool is described in U.S. Pat. No. 4,211,510 to Hopkins who uses it in a boring head. Swiss Pat. No. 270,609 of Engensperger appears to show a milling head comparable to that of Hopkins. In U.S. Pat. No. 3,961,857, Koblesky also shows the use of this type of mounting in a boring bar. In U.S. Pat. No. 3,146,641, Benjamin, et al. show the concept employed in a recessing tool. Finally, in U.S. Pat. No. 2,253,085 Morrell shows the concept applied in a tool for cutting washers from a sheet of material.
None of the above patents teaches or suggests the use of counterbalancing the tool.
Various mechanisms for providing counterbalancing are described in the following patents.
In U.S. Pat. No. 4,040,315, Bellingham shows counterweights that are radially movable, within limits in slots.
In U.S. Pat. No. 4,184,391, Eckle also shows a counterweight that is slidable radially in a guide.
In U.S. Pat. No. 3,180,187, McFerren shows a counterweight that is slidable radially in a channel.
Finally, in U.S. Pat. No. 3,739,666, Wright, et al. show a tube cutting head in which a fixed counterweight is located on the body of the tool.
As will be seen below, the counterbalancing mechanisms used in these patents are completely different in nature from that used in the present invention.
The patents referred to above are discussed at greater length in an Information Disclosure Statement lodged in the file of this application.